等待并且在灯设置为绿色之前不执行功能 [英] Wait and don't execute a function until a light is set to green

问题描述

我知道我们可以使用 .then 来确保异步调用的顺序:

I understand that we could use .then to make sure the order of asynchronous calls:

return doTask1()
    .then(function () {
        return doTask2()
    })

但有时有一个灯会很方便，并且可以说:等待并且不要执行task2，直到灯设置为绿色；灯是一个初始设置为RED的变量，可以通过task1或其他函数设置为GREEN.

But sometimes it will be convenient to have a light and to be able to say: wait and don't execute task2 until a light is set to GREEN; the light is a variable initially set to RED, and can be set to GREEN by task1 or other functions.

有没有人知道是否有可能做到这一点?

Does anyone know if it is possible to accomplish this?

我认为当我们需要结束多个任务以设置浅绿色，并且我们不知道/不介意顺序时，能够表达这一点特别有用这些任务..then 不能轻易做到这一点，因为我们不知道这些任务的顺序.

Edit 1: I think being able to express this is particularly useful when we need several tasks to be ended to set the light green, and we don't know/mind the order of these tasks. .then cannot do this easily, because we don't know the order of these tasks.

编辑 2:关于 my light，我问了 一个更具体的问题.一句话，我们正在等待的是另一个应用程序 B 通过 postMessage 发送的消息.目前，我已经编写了以下代码(在 resolve 中)，它或多或少地起作用(我还没有尝试过，如果只用它们的公共部分制作一个函数就可以工作).

Edit 2: Regarding my light, I had asked a more specific question. In one word, it is the message another application B sends by postMessage that we are waiting for. At the moment, I have written the following code (which is in a resolve), which works more or less (I have not tried if making only ONE function with their common part will work).

task1: ['codeService', '$window', '$q', function (codeService, $window, $q) {
    return codeService.task1().then(function () { // task1 sends a request to another application B by postMessage
        var deferred = $q.defer();
        $window.addEventListener("message", function (event) {
            if (event.data.req === "task1ReturnFromB") deferred.resolve(event.data)
        }, { once: true });
        return deferred.promise
    })
}],
task2: ['codeService', 'task1', '$window', '$q', function(codeService, task1, $window, $q) {
    return codeService.task2().then(function () { // task2 sends a request to Application B by postMessage
        var deferred = $q.defer();
        $window.addEventListener("message", function (event) {
            if (event.data.req === "task2ReturnFromB") deferred.resolve(event.data) 
        }, { once: true });
        return deferred.promise
    })
}]

因此在这种特定情况下，应用程序 B 发送的 postMessage 触发了该事件.在更一般的情况下，我想我们可能会在一个应用程序中通过例如 dispatchEvent 来触发一个事件?

So in this specific case, postMessage sent by Application B triggers the event. In a more general case, I guess we could probably trigger an event by eg, dispatchEvent, in one application?

推荐答案

你没有告诉我们任何关于你的灯的 API，所以我只能猜测它是什么样的.假设它是一个事件驱动模型，您可以将其转换为承诺，然后执行以下操作:

You haven't told us anything about the API for your light so I can only guess what it's like. Presuming it's an event driven model, you can convert it to a promise, and do this:

function waitForGreenLight() {
    return new Promise(function (resolve) {
        $window.addEventListener("message", function (event) {
           if (event.data.req === "task2ReturnFromB") {
               resolve(event.data) 
           }
        }, { once: true });
    });
}

return doTask1()
    .then(waitForGreenLight)
    .then(doTask2);

如果你的灯不提供事件，你可以有一个 waitForGreenLight 定期轮询它直到它变成绿色.使用 waitForGreenLight 的代码将保持不变.

If your light doesn't provide events, you could have a waitForGreenLight that periodically polls it until it's green. The code to use waitForGreenLight would remain the same.

function waitForGreenLight() {
    return new Promise(function (resolve) {
        var handle = setInterval(function () { 
            if (myLight.color === 'green') { 
                resolve();
                clearInterval(handle);
            }
        }, 100);
    });
}

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